Signaling system



Jan. 12, 1943. D. K. GANNETT SIGNALING SYSTEM Fil-ed 0ct. 25, 1940GOA/STAN 7' OUTPUT L AMPLIFIER m/mv 70R 0. K. GAN/VET 7' A T-TORNEYPatented Jan. 12, 1943 SIGNALING SYSTEM Danforth K. Gannett, MountainLakes, N. J assignor to Bell Telephone Laboratories, Incorporated, NewYork,N. Y., a corporation of New York Application October 25, 1940,Serial No. 362,780

6 Claims. (01. 179-84) This invention is a signal device which isoperatively responsive to application of signaling currents ofsinusoidal wave form and which is operatively non-responsive toapplication of cur-. rents of other wave forms.

According to a feature of the invention, false signal operation isprevented in a voice frequency signaling system by distinguishingbetween signaling currents which are of sine wave form and voicecurrents which have a relatively high peak factor. That is, the ratio ofthe maximum to the root-mean-square amplitude of sine wave signalingcurrent is low enough compared with the ratio of the maximum to theroot-meansquare amplitude of voice currents, so that this difference maybe used to prevent false signal operation in response to voice currents.

Another feature of the invention is a signal receiver subjected at timesto voice currents and at other times to voice frequency signalingcurrents of substantially sine wave form, the receiver comprising aconstant output amplifier, connected to a line through which the voiceand signal currents are transmitted, and a biased detector for effectingthe operative energization of a signal relay in response to signalingcurrent without effecting operation of the relay when voice currents arebeing transmitted.

A signal receiver arranged in accordance with the invention is shown inthe drawing which quencies or voice frequency bands and through whichspeech currents may be transmitted.

The signal receiver SR consists of a constant output amplifier H), atransformer T, potentiometer l3, resistor I4, condenser l5, detector l6,and signal relay 20. Three batteries are shown, battery Bl forenergizing the cathode of tube l5, battery B2 supplying the platevoltage for tube I 6, and battery B3 supplying the grid bias for tubeIS. The amplifier In which is designed to give a constantroot-mean-square output may be similar to that disclosed in Fig. 7 ofthe patent to H. S. Black No. 2,209,955 of August 6, 1940. Although thedetector is is shown as a half-wave detector, it is understood that afull-wave rectifier may be used. The voltage of the grid biasing batteryB3 is such that tube I6 is biased to the cut-off point; and thepotentiometer I3 is set so that, with a sine wave input, the peakvoltages applied by transformer l2 to the grid of tube is just fail toeffect a grid-cathode current. The signal relay 20 is designed andadjusted to be barely operated by the current in the anode-oathodecircuit of tube l6 when a sine wave signaling current is transmittedover line L. When currents having a high peak factor, such as voicecurrents, are transmitted over line L, the peak potentials applied tothe gride of tube H; are much higher and the resulting grid-cathodecurrent causes a drop in potential through resistor I4 which increasesthe grid bias to a value which just permits grid current during thepeaks; and, therefore, only the peaks of the speech waves are rectifiedand the current in the anode circuit is insufficient to energize thesignal relay 20. The operation of relay 20, responsive to signalingcurrent, closes a circuit through conductors 2| and 22 to effect anydesired result.

The performance of such a signal receiving arrangement may be analyzedby assuming that the signaling currents have a pure sine wave form andthat the voice currents consist of rectangular impulses of alternatepolarity, each impulse having an amplitude h and lasting for a smallfraction k of a half cycle. The output of the detector IS in response tosuch a rectangular wave having a high peak factor will be compared tothe output in response to a sine Wave. The characteristics of the twowaves are as follows:

and the ratio of peak factors 1 R=T V210 Assuming further that theconstant rootmean-square value of the output of the amplifier ill, ofeither wave, is B, then for the sine wave,

and for the rectangular wave B ME =B or h=fi Since, from the ratio ofthe peak factors,

and therefore it 2 RB Now assume that the detector i5 is a linear fullwave rectifier. The current through signal relay 29, responsive to asine Wave input, is

to a rectangular wave input, is

and this is the factor by which the current through relay is reducedwhen a rectangular wave, whose peak factor is R times that of a sinewave, is applied instead of a sine wave. For instance, if R=2.5,

Or expressing it difierently, ii the rectangular wave has a peak factor8 decibels higher than that of a sine wave, the relay current is 18decibels less. This indicates that there is an ample margin between theoperating current through relay 29 responsive to signaling current andthe non-operating current through this relay responsive to voicecurrent.

The invention is not limited in its application to voice frequencysignaling but is generally applicable to any signaling system in whichsignal operation is desired in response to sinusoidal signal currentsbut not in response to currents having a different wave form. Althoughthe specific arrangement shown in the drawing comprises an amplifierhaving a constant root-meansquare output and a detector responsive tothe peak value of the applied currents, the arrangement mightalternatively comprise an amplifier of constant peak output and adetector responsive to the root-mean-square value of the appliedcurrents.

What is claimed is:

1. In a signaling system including a line subjected to voice currentsand to signals consisting of voice frequency currents, the wave form ofthe signaling current being that of a sine wave, a signal receiver, saidreceiver comprising a signal relay, means including a, detector and aconstant output amplifier in series connecting said relay to said linefor response to incoming signals, said line being connected to the inputconductors of said amplifier and the output conductors of said detectorbeing connected to said relay, and means for biasing the detector andfor increasing the bias when the input voltage exceeds the maximumvoltage applied thereto by sine wave signal currents, thereby to preventthe operation of said signal relay in response to voice currents.

2. In a signaling system, a signal receiver operatively responsive tosignals consisting of alternating currents the wave form of which issuch that the ratio of the peak amplitude to the root-meansquareamplitude does not exceed a certain value and operatively non-responsiveto alternating currents the wave form of which is such that the ratio ofthe peak amplitude to the root-meansquare amplitude does exceed saidcertain value, said receiver comprising an amplifier for receiving thesignaling currents, said amplifier having a constant output, a detectorwhose sensitivity is in inverse relation tothe amplitude of the appliedvoltage, said detector being connected to the output conductors of saidamplifier, and a signal responsive device connected to the outputterminals of said detector.

3. In a signaling system, a signal receiver subjected to voice currentsand to signals consisting of voice frequency current of substantiallysine wave form, said receiver comprising a constant output amplifier towhich voice currents and Signal currents are applied, a relay, and adetector connecting said relay to said amplifier for operation inresponse to signal currents, said detector comprising an anode, acathode and a control grid, means biasing said detector to just preventcurrent in its grid-cathode circuit when signal current is being appliedto said amplifier, and means for increasing the grid bias when voicecurrents are applied to said amplifier thereby to prevent the operationof said relay.

4. In a signaling system, a signal receiver subiected to voice currentsand to signals consisting of voice frequency current of substantiallysine wave form, said receiver comprising a constant output amplifier towhich voice currents and signal currents are applied, a detectorcomprising an anode, a cathode and a control grid, a signal responsiverelay in the output circuit of said detector, means comprising atransformer and a potentiometer connecting the output of said am plifierto the grid-cathode circuit of said detector, a biasing battery, meanscomprising said potentiometer and said battery for just preventinggrid-cathode current in said detector when signal currents are applied,and means comprising a resistor in series with the grid of said detectorfor increasing the grid bias when voice currents are applied, thereby topermit only the peaks of voice currents to be applied to said relay,said relay being adjusted to be responsive to the current in the outputcircuit of said detector resulting from the application of signalcurrent but nonresponsive to the current in the output circuit of saiddetector resulting from the application of voice current.

5. A signal receiver comprising a constant output amplifier having aninput circuit for receiving signals, a signal relay for operationresponresponse to current other than signaling current in the inputcircuit of said amplifier.

6. A signal receiver comprising an amplifier having an input circuit forreceiving signals, said amplifier being arranged to have a constantrootmean-square output, a. signal relay for responding to sine wavesignaling currents, means comprising a biased detector for operativelyconnecting said amplifier to said relay, the current in the outputcircuit of said detector being normally in- 10 efiective to operate saidrelay and eifective when the current in the input circuit of saidamplifier is sine wave signaling current to operate said relay, andmeans increasing the bias of said detector when there is current of waveform other than sine wave form in the input circuit of said amplifier,thereby to prevent the operation of said relay.

DANFORTH K. GANNE'IT.

